Introduction
The International Telegraph and Telephone Consultative Committee (CCITT), an international communications standards organization, has been developing a standard for 16 kb/s speech coding and decoding for universal applications. The standardization process included the issuance by the CCITT of a document entitled "Terms of Reference" prepared by the ad hoc group on 16 kbit/s speech coding (Annex 1 to question 21/XV), June 1988.
Presently, the candidate being considered for the standard is Low-Delay Code Excited Linear Predictive Coding (hereinafter, LD-CELP) described in substantial part in the incorporated application Ser. No. 07/298451. Aspects of this coder are also described in J-H Chen, "A robust low-delay CELP speech coder at 16 kbit/s, "Proc. GLOBECOM, pp. 1237-1241 (Nov. 1989); J-H Chen, "High-quality 16 kb/s speech coding with a one-way delay less than 2 ms, "Proc. ICASSP, pp. 453-456 (April 1990); J-H Chen, M. J. Melchner, R. V. Cox and D. O. Bowker, "Realtime implementation of a 16 kb/s low-delay CELP speech coder, "Proc. ICASSP, pp. 181-184 (April 1990); all of which papers are hereby incorporated herein by reference as if set forth in their entirety. The patent application Ser. No. 07/298,451 and the cited papers incorporated by reference describe aspects of the LD-CELP system as evaluated in Phase 1. Accordingly, the system described in these papers and the application Ser. No. 07/298,451 will be referred to generally as the Phase 1 System.
A document further describing the LD-CELP candidate standard system was presented in a document entitled "Draft Recommendation on 16 kbit/s Voice Coding," submitted to the CCITT Study Group XV in its meeting in Geneva, Switzerland during Nov. 11-22, 1991 (hereinafter, "Draft Recommendation"), which document is incorporated herein by reference in its entirety. For convenience, and subject to deletion as may appear desirable, part or all of the Draft Recommendation is also attached to this application as Appendix 1. The system described in the Draft Recommendation has been evaluated during Phase 2 of the CCITT standardization process, and will accordingly be referred to as the Phase 2 System. Other aspects of the Phase 2 System are also described in a document entitled "A fixed-point Architecture for the 16 kb/s LD-CELP Algorithm" (hereinafter, "Architecture Document") submitted by the assignee of the present application to a meeting of Study Group XV of the CCITT held in Geneva, Switzerland on Feb. 18 through Mar. 1, 1991. The Architecture Document is hereby incorporated by reference as if set forth in its entirety herein and a copy of that document is attached to this application for convenience as Appendix 2. Also incorporated by reference as descriptive of the Phase 2 System and J. H. Chen, Y. C. Lin, and R. V. Cox, "A fixed point 16 kb/s LD-CELP Algorithm," Proc. ICASSP, pp. 21-24, (May 1991).